Be careful of your posture when using your computer keyboard: make sure you are not leaning forward and that the screen is at proper eye level.
When doing housework or yard work, consciously tighten your abdominal muscles, especially when bending and when raking or using a vacuum cleaner.
When driving, put your seat close enough to the steering wheel so your arms are not stretched out and your neck is not craned forward.
When walking your dog, be sure to avoid getting pulled by using a special halter that will feel fine to your dog but will not allow undue tugging (available at pet supply stores and catalogs).
If you have to stand in one spot for long periods of time, invest in a small mat that will cushion your feet and thus every other joint in your body.
If you have to sit for long periods of time, make believe you are getting up often (fool your body) by twisting left and right and by shifting from one side of the buttocks to the other. This will keep discs limber and keep you from getting stiff.
If you don't feel that your abdominal muscles are very strong, purchase a low back support belt from the drug store or your chiropractor. Worn properly (very low - below the waist) you should have more stamina.
When lying down, place a small rolled hand towel under your neck. It's even more effective if you can fall asleep in this posture and will help your neck curve as well as reduce upper and low back pain.
Very light weightlifting is effective for avoiding back pain. Buy three pound dumbbells (or lighter if necessary), lie on your back with knees bent, and lift your arms straight up and down ten times. Do it slowly and carefully and do it every day.
Avoid sugar to avoid muscle and joint aches. Be careful because sugar is hidden in lists of ingredients. However, if you see it listed first - in all its many names - you can be sure that it is the primary ingredient. Be careful also of foods that contain dyes and artificial food coloring.